Question

PLZ HELP! A train averages a speed of 90 miles per hour across the plains and 37.5 miles per hour through the mountains. If a trip of 300 miles took 3 hour and 48 minutes, how much of it was through the mountains?

Answer 1

Answer:

3.8

Step-by-step explanation:

A train averages a speed of 90 miles per hour across the plains and 37.5 miles per hour through the mountains.

If a trip of 300 miles took 3 hour and 48 minutes, how much of it was through the mountains?

Let d = distance traveled at 37.5 (thru the mountains)

then

(300-d) = distance traveled at 90 mph

Write a time equation, time = dist/speed

change 3 hr 48 min to hrs: 3 + 48/60 = 3.8 hrs

plain time + mountain time = 3.8 hrs

%28300-d%29%2F90 + d%2F37.5 = 3.8

Multiply 90*37.5

3375*%28300-d%29%2F90 + 3375*d%2F37.5 = 3.8(3375)

cancel the denominator

37.5(300-d) + 90d = 12825

11250 - 37.5d + 90d = 12825

52.5d = 1575

d = 1575/52.5

d = 30 mi thru the mountains

Check this, find the distance on the plain

300-30 = 270 mi

Find the actual time at each speed

270/90 = 3 hrs

30/37.5 = .8 hrs

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total time: 3.8 hrs